Pipe-in-pipe pipelines, also known as PIP pipelines, are well known in the art, and generally comprise, with reference to the accompanying prior art FIG. 1, an outer pipe 1 (or “carrier pipe”) and a usually concentric or co-axial inner pipe or flowline 2. An annular space or “dry annulus” is defined between the inner and outer pipes. The inner pipe 2 is used to transport or convey fluids such as hydrocarbons, in particular oil and gas, between two or more static and/or moveable locations. This includes conveying fluids between vessels, or locations at or near a seabed such as an oil head, in particular a remote oil head, to an underwater facility and/or to a riser towards sea level, and/or directly to an onshore facility.
Bundle pipelines are also well known in the art and generally comprise an outer pipe (or “casing pipe”) and a combination of inner pipes, with annular space thereinbetween. The inner pipelines may comprise at least one flowline used to transport or convey fluids such as hydrocarbons, in particular oil and gas, between two or more static and/or moveable locations. Other inner pipes can be used for, but are not limited to, water injection, gas lift and chemical injection. Umbilical cables can also be included in a bundle pipeline.
It is possible to insert cables in the dry annulus created between such various inner and outer pipes. Umbilical cables are well known to be inserted with a bundle pipeline system, for example for control and electrical feeding of remote structures. Monitoring cables such as, but not limited to, optical fibres can also be placed in the annular space between the inner and outer pipes to provide monitoring of one or more parameters such as for example temperature, pressure or deformations.
Moreover, fluids circulating along deepwater or long tie-back flowlines may experience a significant temperature drop, leading to the risk of hydrate plugging and wax formation, especially in oil and gas flows. PIP and bundle pipelines can address the problem of hydrate or wax plugging without having to access the interior of the inner flowline. Active heating is typically implemented by a method known as ‘trace heating’, whereby electrical cables, which may be round or flat cables, are placed in the annular space between the inner and outer pipes to provide heat for maintaining the required temperature level of the fluid inside the inner pipe. A PIP pipeline with a trace heating arrangement is also known as a ETH-PIP pipeline (electrically trace heated pipe-in-pipe).
For the purpose of the present description, the term cables includes all types of elongate cables designed to run co-axially within a pipeline, being separate or attached with one or more inner pipes, and including but not limited to umbilical, optical, trace heating or electrical cables.
Cables in the annular space of a pipeline require a connection to a power or control supply. Typically, a subsea feeding system is arranged alongside the pipeline, including feed umbilical connectors and optionally a subsea transformer for electrical power system. The feeding system is usually connected to a topside control unit, and for power application, to an electrical power production facility.
The cables in the pipeline are typically connected to the feeding system at an end region of the cabled pipeline, also termed a pipeline end termination (PLET), via a connector arrangement, which can form an integral part of PLET and acts as the gateway between the pipeline cable system and the external power or control unit. The connector arrangement can also form an integral part of an in-line tee or in-line tee assembly (ILT/ITA) characteristically placed at mid-line pipeline location.
The purpose of the connector arrangement is to make the connection between the cables and a subsea umbilical termination arrangement (SUTA) of the subsea feeding umbilical, while maintaining a leak-proof barrier between the hydrostatic wet subsea environment and the dry annulus of the pipeline at atmospheric pressure. Preservation of the ‘leakproof-ness’ of the dry annulus is of utmost importance in this arrangement as the main disadvantages associated with connector junctions include low levels of redundancies associated with leak prevention.
Hitherto, elastomeric seals are typically used for sealing the connections between the dry annulus and the wet environment in conventional connector arrangements such as that shown in GB2416016A. However, the performance of such seals in the long term has been questioned.
GB2416016B describes a mid-line connector for pipe-in-pipe electrical heating, based on outer body and inner body forgings brought together to form a single ‘connector’, having a single dry interior area, and having pre-formed connection pockets with elastomeric seals. As well as only using elastomer seals, the forgings are also not easily changeable for other configurations, and the connector must be inserted between two inner and outer pipes of a PIP pipeline only having an electrical current-based heating system.
It is an object of the present invention to provide an improved connector arrangement for connecting cables (preferentially electrical or optical cables) in an annular space between inner and outer pipes of a pipeline to an external assembly, such as for example a power supply, monitoring unit or control unit.